Transfer or delivery hoses for cryogenic liquids such as liquified natural gas are normally insulated to least minimize heat transfer from the ambient environment to the cryogenic liquid and to protect the operator from the cold temperatures normally encountered. Because of the wide temperature changes during cool-down and warm-up cycles and the number of such cycles, condensation of water within the insulation can be a significant problem. Such condensation within the insulation can significantly reduce, and even destroy, the insulating properties of many insulating materials. Such condensation within the insulation can also significantly increase the cool-down refrigeration requirements by requiring the water trapped within the insulation to be refrozen during every cool-down cycle. Such condensation can also significantly reduce the flexibility of the transfer or delivery hose due to ice formation within the insulation. Such a "frozen" hose and insulating system, if forced into a different configuration by an operator, can be damaged or even destroyed.
Attempts to prevent the condensation of water within the insulation have usually involved the use of vapor barriers over the insulation to prevent water from entering the insulation. Such vapor barriers, however, break down over time and allow moisture to enter the insulation. The insulation may become saturated with water, thereby significantly reducing the effectiveness of the insulation. Once the insulation becomes wet, the vapor barrier will tend to trap moisture within the insulation and make it very difficult, if not impossible, to dry the insulation. Thus, once the insulation is saturated, it may become necessary to replace the insulation or scrap the hose assembly. Vapor barriers used in cryogenic liquid transfer operations generally break down especially quickly due to the wide temperature swings, the repeated flexing of the hose and insulation material, and the numerous cool-down cycles normally associated with such operations. Thus, and especially when used with cryogenic liquids, the use of vapor barriers to prevent water from entering the insulation has not been as successful as desired.
Metal vapor barriers have also been used to prevent water from saturating the insulation in cryogenic liquid transfer operations. Such vapor barriers generally are constructed with an outer surface of a relatively flexible metal material. But as the thickness of the vapor barrier increases, its flexibility generally decreases. Metal vapor barriers with sufficient flexibility are generally very expensive to produce. Furthermore, insulating systems using such metal vapor barriers cannot easily be adapted for differing hose configurations often found in the field. Metal sheaths used as vapor barriers can also significantly increase the weight of the delivery hose system.
Even where effective vapor barriers are provided, moisture will eventually find its way into the insulation through weak points in the system (e.g., joints, points of attachment of the hose to the storage unit or nozzle, and the like). Such moisture will build up within the insulation over time due largely to the effectiveness of the vapor barrier in preventing the trapped moisture from escaping. Thus, over time the effectiveness of the insulation can be destroyed even though the vapor barrier remains intact.
Vacuum jacketed hoses generally provide excellent insulation but are heavier, stiffer, and much more expensive than conventional single hoses. Furthermore, such vacuum jacketed hoses cannot easily be repaired in the field. Their use in cryogenic liquid transfer is, therefore, limited to special applications.
It would be desirable, therefore, to provide a flexible, lightweight, non-water absorbing insulation material for use in cold liquid transfer operations and especially in cryogenic liquid transfer operations. It would also be desirable to provide an insulation system which would allow any condensed water to gravity drain from the system. It would also be desirable to provide an inexpensive insulation system which can be easily adapted in the field for installation in widely differing liquid transfer systems and which can easily be repaired in the field. The present invention provides such an insulation system.